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  • 1. Bouton, Anthony
    et al.
    Vennin, Emmanuelle
    Pace, Aurélie
    Bourillot, Raphaël
    Dupraz, Christophe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Thomazo, Christophe
    Brayard, Arnaud
    Désaubliaux, Guy
    Visscher, Pieter T.
    External controls on the distribution, fabrics and mineralization of modern microbial mats in a coastal hypersaline lagoon, Cayo Coco (Cuba)2016In: Sedimentology, ISSN 0037-0746, E-ISSN 1365-3091, Vol. 63, no 4, p. 972-1016Article in journal (Refereed)
    Abstract [en]

    Active, carbonate-mineralizing microbial mats flourish in a tropical, highly evaporative, marine-fed lagoonal network to the south of Cayo Coco Island (Cuba). Hypersaline conditions support the development of a complex sedimentary microbial ecosystem with diverse morphologies, a variable intensity of mineralization and a potential for preservation. In this study, the role of intrinsic (i.e. microbial) and extrinsic (i.e. physicochemical) controls on microbial mat development, mineralization and preservation was investigated. The network consists of lagoons, forming in the interdune depressions of a Pleistocene aeolian substratum; they developed due to a progressive increase in sea-level since the Holocene. The hydrological budget in the Cayo Coco lagoonal network changes from west to east, increasing the salinity. This change progressively excludes grazers and increases the saturation index of carbonate minerals, favouring the development and mineralization of microbial mats in the easternmost lagoons. Detailed mapping of the easternmost lagoon shows four zones with different flooding regimes. The microbial activity in the mats was recorded using light-dark shifts in conjunction with microelectrode O-2 and HS- profiles. High rates of O-2 production and consumption, in addition to substantial amounts of exopolymeric substances, are indicative of a potentially strong intrinsic control on mineralization. Seasonal, climate-driven water fluctuations are key for mat development, mineralization, morphology and distribution. Microbial mats show no mineralization in the permanently submersed zone, and moderate mineralization in zones with alternating immersion and exposure. It is suggested that mineralization is also driven by water-level fluctuations and evaporation. Mineralized mats are laminated and consist of alternating trapping and binding of grains and microbially induced magnesium calcite and dolomite precipitation. The macrofabrics of the mats evolve from early colonizing Flat mats to complex Cerebroid or Terrace structures. The macrofabrics are influenced by the hydrodynamic regime: wind-driven waves inducing relief terraces in windward areas and flat morphologies on the leeward side of the lagoon. Other external drivers include: (i) storm events that either promote (for example, by bioclasts covering) or prevent (for example, by causing erosion) microbial mat preservation; and (ii) subsurface degassing, through mangrove roots and desiccation cracks covered by Flat mats (i.e. forming Hemispheroids and Cerebroidal structures). These findings provide in-depth insights into understanding fossil microbialite morphologies that formed in lagoonal settings.

  • 2. Fontana, Simone
    et al.
    Nader, Fadi Henri
    Morad, Sadoon
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Ceriani, Andrea
    Al-Aasm, Ihsan Shakir
    Daniel, Jean-Marc
    Mengus, Jean-Marie
    Fluid-rock interactions associated with regional tectonics and basin evolution2014In: Sedimentology, ISSN 0037-0746, E-ISSN 1365-3091, Vol. 61, no 3, p. 660-690Article, review/survey (Refereed)
    Abstract [en]

    An integrated approach consisting of fracture analysis, petrography, carbon, oxygen and strontium-isotope analyses, as well as fluid-inclusion micro-thermometry, led to a better understanding of the evolution of fluid-rock interactions and diagenesis of the Upper Permian to Upper Triassic carbonates of the United Arab Emirates. The deposited carbonates were first marked by extensive early dolomitization. During progressive burial, the carbonates were affected by dolomite recrystallization as well as precipitation of vug and fracture-filling dolomite, quartz and calcite cements. After considerable burial during the Middle Cretaceous, sub-vertical north-south oriented fractures (F1) were cemented by dolomite derived from mesosaline to hypersaline fluids. Upon the Late Cretaceous maximum burial and ophiolite obduction, sub-vertical east-west fractures (F2) were cemented by dolomite (Dc2) and saddle dolomite (Ds) derived from hot, highly saline fluids. Then, minor quartz cement has precipitated in fractures from hydrothermal brines. Fluid-inclusion analyses of the various diagenetic phases imply the involvement of increasingly hot (200 degrees C) saline brines (20 to 23% NaCl eq.). Through one-dimensional burial history numerical modelling, the maximum temperatures reached by the studied rocks are estimated to be in the range of 160 to 200 degrees C. Tectonically-driven flux of hot fluids and associated diagenetic products are interpreted to have initiated during the Late Cretaceous maximum burial and lasted until the Oligocene-Miocene compressional tectonics and related uplift. The circulation of such hydrothermal brines led to partial dissolution of dolomites (Dc2 and Ds) and to precipitation of hydrothermal calcite C1 in new (mainly oriented north-south; F3) and pre-existing, reactivated fractures. The integration of the obtained data confirms that the diagenetic evolution was controlled primarily by the interplay of the burial thermal evolution of the basin and the regional tectonic history. Hence, this contribution highlights the impacts of regional tectonics and basin history on diagenetic processes, which may subsequently affect reservoir properties.

  • 3. Gebhardt, Andrea Catalina
    et al.
    Ohlendorf, Christian
    Niessen, Frank
    De Batist, Marc
    Anselmetti, Flavio S.
    Ariztegui, Daniel
    Kliem, Pierre
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Zolitschka, Bernd
    Seismic evidence of up to 200 m lake-level change in Southern Patagonia since Marine Isotope Stage 42012In: Sedimentology, ISSN 0037-0746, E-ISSN 1365-3091, Vol. 59, no 3, p. 1087-1100Article in journal (Refereed)
    Abstract [en]

    Maar lake Laguna Potrok Aike is located north of the Strait of Magellan (south-eastern Patagonia). Seismic reflection profiles revealed a highly dynamic palaeoclimate history. Dunes were identified in the eastern part of the lake at approximately 30 to 80 m below the lake floor, overlying older lacustrine strata, and suggest that the region experienced dry conditions probably combined with strong westerly winds. It is quite likely that this can be linked to a major dust event recorded in the Antarctic ice cores during Marine Isotope Stage 4. The dunes are overlain by a series of palaeo-shorelines indicating a stepwise water-level evolution of a new lake established after this dry period, and thus a change towards wetter conditions. After the initial, rapid and stepwise lake-level rise, the basin became deeper and wider, and sediments deposited on the lake shoulder at approximately 33 m below present-day lake level point towards a long period of lake-level highstand between roughly 53.5 ka cal. bp and 30 ka cal. bp with a maximum lake level some 200 m higher than the desiccation horizon. This highstand was then followed by a regressional phase of uncertain age, although it must have happened some time between approximately 30 ka cal. bp and 6750 yrs cal. bp. Dryer conditions during the Mid-Holocene are evidenced by a dropping lake level, resulting in a basin-wide erosional unconformity on the lake shoulder. A second stepwise transgression between ca 5.8 to 5.4 ka cal. bp and ca 4.7 to 4 ka cal. bp with palaeo-shorelines deposited on the lake shoulder unconformity again indicates a change towards wetter conditions.

  • 4.
    Klaminder, Jonatan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Appleby, P
    Crook, P
    Renberg, Ingemar
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Post-deposition diffusion of 137Cs in lake sediment: implications for radiocaesium dating2012In: Sedimentology, ISSN 0037-0746, E-ISSN 1365-3091, Vol. 59, no 7, p. 2259-2267Article in journal (Refereed)
    Abstract [en]

    Peak activities of radiocaesium (137Cs) in lake sediments have frequently been used to infer the ages of sediments deposited in the 1960s (137Cs derived from nuclear bomb testing) or in 1986 (Chernobyl derived 137Cs). Records of the vertical distribution of 137Cs in sediments can thus be used to provide accurate dates for a critical period in which palaeoecological reconstructions often overlap contemporary monitoring data. However, knowledge regarding how the distribution of 137Cs in sediments is affected by post-depositional processes is limited to interpretations based on the 137Cs distribution in sediments sampled at a single given date. This study assesses the extent to which the 137Cs record in annually laminated (varved) lake sediments is affected by post-depositional diffusion, using 11 archived sediment cores sampled between 1986 and 2007. The sediment record reveals how Chernobyl 137Cs incorporated into the 1986 varve diffused downwards in the core at a decreasing rate over time, whereas the surface sediments continued to receive inputs of 137Cs mobilized from the catchment soils or lake margin. In spite of these processes, all cores post-dating the Chernobyl accident had a clear and well-resolved peak in the 1986 varve, justifying the use of this feature as a fixed chronostratigraphic feature. Because of the very high levels of Chernobyl fallout at this site, downwards migration of Chernobyl 137Cs has, however, completely masked the nuclear weapons 137Cs fallout peak that had been clearly preserved in the 1964 varve of a pre-Chernobyl core sampled just three weeks before the Chernobyl accident. In consequence, the weapons fallout marker is likely to be of little use for determining 137Cs dates in areas strongly affected by high levels of Chernobyl fallout.

  • 5.
    Stevens, Thomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Lu, Huayu
    Optically stimulated luminescence dating as a tool for calculating sedimentation rates in Chinese loess: comparisons with grain-size records2009In: Sedimentology, ISSN 0037-0746, E-ISSN 1365-3091, Vol. 56, no 4, p. 911-934Article in journal (Refereed)
  • 6.
    Tafesse, Solomon
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Fernlund, Joanne M. Robison
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Sun, Wenjuan
    Bergholm, Fredrik
    KTH, School of Technology and Health (STH), Medical Engineering.
    Evaluation of image analysis methods for the quantification of particle angularityIn: Sedimentology, ISSN 0037-0746, E-ISSN 1365-3091Article in journal (Other academic)
  • 7.
    Tafesse, Solomon
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Robison Fernlund, Joanne M.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    Sun, Wenjuan
    Bergholm, Fredrik
    KTH, School of Technology and Health (STH), Medical Engineering.
    Evaluation of image analysis methods used for quantification of particle angularity2013In: Sedimentology, ISSN 0037-0746, E-ISSN 1365-3091, Vol. 60, no 4, p. 1100-1110Article in journal (Refereed)
    Abstract [en]

    Angularity is an important parameter in the characterization of particle morphology that is used to interpret the transport history of particles in sedimentary deposits. In the past, visual classification using silhouette charts was widely used to determine particle angularity, but this approach is subjective and time-consuming. With advances in modern image analysis techniques and low-cost software packages, it is possible to rapidly quantify particle angularity more objectively than using visual classification methods. This study re-examines the performance of three existing image analysis methods and one new image analysis procedure, applied to six rock and sediment samples that were visually different in angularity. To facilitate comparison between the angularity results, measurements were reduced to rankings for each aggregate sample. These results show that the four image analysis methods rank the angularity of the samples differently, and that none rank the mean angularity index in the same order as the angularity ranking using visual classification. Therefore, further research is needed to develop an image analysis method that can quantify the angularity of sedimentary particles more precisely.

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